N,N′-Bis(4-bromophenyl)pyridine-2,6-dicarboxamide

The molecule of the title compound, C19H13Br2N3O2, lies about a twofold rotation axis. The benzene ring makes dihedral angles of 8.9 (2) and 16.4 (2)° with the central pyridine ring and the second benzene ring, respectively. An intramolecular N—H⋯N contact occurs. In the crystal, molecules are connected by pairs of N—H⋯O hydrogen bonds into chains along the c axis.

The molecule of the title compound, C 19 H 13 Br 2 N 3 O 2 , lies about a twofold rotation axis. The benzene ring makes dihedral angles of 8.9 (2) and 16.4 (2) with the central pyridine ring and the second benzene ring, respectively. An intramolecular N-HÁ Á ÁN contact occurs. In the crystal, molecules are connected by pairs of N-HÁ Á ÁO hydrogen bonds into chains along the c axis.

Experimental
Financial assistance for this project by the Higher Education Commission of Pakistan through the International Research Support Initiative Programe (IRSIP) is acknowledged by the authors. characteristic of their chemical structure. It includes a high proportion of aromatic groups and combined double bonds.
The demand for polyamide-imide (PAI) and other high-temperature resistant polymeric materials has grown steadily because of their outstanding mechanical properties, excellent thermal and oxidative stability (Zhong et al., 2002;Sun et al., 2006). Incorporation of heterocylic groups in the polymer backbone is a rational approach which promotes solubility without affecting thermal and mechanical properties to any great extent (Diakoumakos et al., 1994, Hamciuc et al., 2001. As part of our enduring interest in solubility of aromatic poly(amide-imide)s by structural modification, we are reporting a pyridine-based monomer having inbuilt amide functionality. It enhances the solubility of resulting poly(amidimide)s without worsening the inherent properties of the polymer.

Experimental
In this preparation, chemicals of reagent grade quality were used without their further purification. In a 100 ml threenecked round-bottomed flask, equipped with a condenser, a nitrogen gas inlet tube, a thermometer and a magnetic stirrer, 0.02 mole (3.44 g) of 4-bromoaniline in 25 mL of dry tetrahydrofuran (THF) were stirred at 273-278 K for 30 minutes and 0.01 mol (2.04 g) of pyridine-2,6-dicarbonyl dichloride in 30 mL of THF was added dropwise by dropping funnel.
Stirring was continued for further 1 h at the same conditions. The temperature of reaction mixture was then raised to 308-313 K and stirring was continued for 45 minutes. The flask content was cooled to room temperature, poured into water and left for 24 h. Resulting dark brown precipitate was filtered, washed with hot water and 5% NaOH solution. Finally, product was washed with hot water and methanol, dried under vacuum at 353 K. The crude product was recrystallized from THF-ethylacetate mixture (1:2).

Refinement
Hydrogen atoms were identified in difference syntheses, and then refined at idealized positions riding on the carbon or nitrogen atoms with C-H = 0.95 Å and N-H = 0.88 Å and isotropic displacement parameters U iso (H) = 1.2U(C/N eq ).

Figure 2
Crystal packing viewd along b axis with hydrogen bonds as dotted lines. H-atoms not involved are omitted. Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.